Thirty minutes to a healthy heart

Sun 19 Feb 2017

Even a single workout could be good for the heart. That’s the conclusion of a fascinating new study in mice that found that 30 minutes on a treadmill affects gene activity within cardiac cells in ways that, over the long haul, could slow the aging of the animals’ hearts.

Although the study involved mice, the results may help to explain just how, at a cellular level, exercise improves heart health in people as well.

There’s no question that, in general, physical activity is good for hearts. Still, researchers have remained puzzled about just how exercise alters hearts for the better. Exercise is known to improve our blood pressure, pulse rate and cholesterol profiles, all of which are associated with better cardiac health.

But many scientists who study the links between exercise and heart health have pointed out that these changes, considered together, explain only about half the reported statistical reductions in cardiac disease and death.

Other, more complex physiological modifications must simultaneously be taking place within the heart itself during and after exercise, these researchers have speculated.

Focus on telomeres

And recently, researchers at the University of Maryland in College Park and other institutions have begun to wonder whether some of these changes might involve telomeres. Telomeres are tiny caps on the ends of chromosomes, often compared to the tips of shoelaces, which help to prevent fraying and damage to our DNA. Young cells have relatively long telomeres. As a cell ages or undergoes significant stress, its telomeres shorten. If they become too abbreviated, the cell stops working well or dies.

Aerobic exercise, in particular, affects telomeres. In past studies, master athletes have been shown to have longer telomeres in their white blood cells than sedentary people of the same chronological years, suggesting that at a cellular level, the athletes are more youthful.

But while it is easy to obtain and look inside white blood cells, far less has been known about telomeres within cardiac cells.

So for the new study, which was published this month in Experimental Physiology , the Maryland researchers and their colleagues turned to young, healthy female mice. (They chose females because they tend to run more readily than males.) The researchers wished to see what happens inside heart muscle cells after a single workout. So they taught some of the animals how to run comfortably on small treadmills and then returned them to their cages for several days so that their bodies would lose any aerobic conditioning. Other mice remained sedentary as a control group.

Then the runners were placed back on the treadmills, where they ran at a tolerable intensity (in mouse terms) for 30 minutes, a workout designed to simulate moderate exercise in people. Researchers took tissue samples of the animals’ hearts either immediately after they had finished running or an hour later, and also gathered samples from sedentary mice.

The scientists looked for changes within the animals’ cardiac cells in the levels of certain proteins that are known to directly prevent telomeres from shortening. They also looked at the activity of other genes that help to keep DNA in good repair. These genes release proteins that are thought to help cells adapt to the physiological stress of exercise and, in the process, also indirectly maintain telomere health.

It turned out that immediately after a single 30-minute jog, the runners’ heart cells were noticeably different from those of the animals that had not moved. In particular, they showed higher levels of the proteins directly related to telomere length. These findings indicate that a single, moderate workout beneficially alters telomere biology in the heart, says Andrew Ludlow, who was a doctoral candidate at the University of Maryland and lead author of the study.NYT